The present invention relates to cellular coal products produced from coal powder and to their methods of production. Products utilizing the coal-based porous products are also described.
ASTM standards DD5515-97, xe2x80x9cStandard Test Method for the Determination of Swelling Properties of Bituminous Coalxe2x80x9d and D720-91 xe2x80x9cStandard Test Method for Free Swelling Index of Coalxe2x80x9d both define conditions for measuring the inherent property of coals to xe2x80x9cswellxe2x80x9d upon heating in an uncontrolled combustion situation. Hence, the propensity of coal to swell is well known in the prior art. To the best of our knowledge, however, no one has attempted to take advantage of this property of coals to swell by controllably xe2x80x9cswellingxe2x80x9d a coal product to obtain a highly useful, low density, porous carbon product.
Similarly, very sophisticated processes have been developed for the production of cellular foamed carbon products. Such processes often involve the use of blowing agents and the application of very high pressures in the fabrication process, and many use highly sophisticated starting materials. These materials, while very lightweight and demonstrating superior strength, tend to be relatively costly, either due to the nature of their starting materials and/or the complexity of their fabrication processes.
There exists a wide and varied class of requirements for low-density materials in the construction, aerospace, transportation, metal processing and other industries for which low-density materials are constantly being developed. Many of these materials exhibit properties such as fire resistance that make them uniquely suited to their end use application. In many applications, however, the aforementioned relatively high cost, low-density materials cannot be used because the final application will simply not justify their relatively high cost.
Accordingly, it would be most desirable if a relatively low cost, low-density material demonstrating many of the desirable characteristics of the aforementioned products, such as fire resistance, were available.
It is therefore an object of the present invention to provide a relatively low cost, low density product that is suited to application in the construction, aerospace, transportation, metal processing and other industries where such properties are desired.
It is another object of the present invention to provide a simple and low cost method for the production of such products.
According to the present invention there are provided coal-based cellular or porous products having a density of preferably between about 0.1 g/cm3 and about 0.8 g/cm3 that are produced by the controlled heating of coal particulate preferably up to xc2xc inch in diameter in a xe2x80x9cmoldxe2x80x9d and under a non-oxidizing atmosphere. According to a specifically preferred embodiment, the starting material coal has a free swell index as determined by aforementioned ASTM D720 test of between about 3.5 and about 5.0. The porous product thereby produced, preferably as a net shape or near net shape, can be machined, adhered and otherwise fabricated to produce a wide variety of low cost, low density products, or used in its preformed shape as a filter, heat or electrical insulator etc. Such cellular products, without further treatment and/or the addition of strengthening additives have been shown to exhibit compressive strengths of up to about 4000 psi. Impregnation with appropriate materials or the incorporation of various strength improving additives can further increase the compressive, tensile and other properties of these cellular materials. Further treatment by carbonization or graphitization yields cellular products that can be used as electrical or beat conductors.